KATOWICE, Poland (Reuters) – United Nations’ climate talks to agree on the rules of the 2015 Paris Agreement dragged on into an extra day on Saturday as ministers tried to overcome the last political hurdles after working through the night.

The schedule for the closing plenary, when sparks could fly among nations if there are issues in the text still open to opposition, has been repeatedly pushed back to later in the day – a sign a more diplomacy work needs to be done.

Some exhausted negotiators were seen leaving the conference venue in Katowice, Poland, in the early hours of Saturday morning to get a few hours’ rest but many ministers worked through the night to try and iron out differences.

Despite this, European climate commissioner Miguel Arias Canete seemed optimistic on Saturday morning.

“UN climate talks go into overtime. Latest version of the draft agreement just out…A deal to make the Paris Agreement operational is within reach,” he tweeted.

The last stumbling blocks have been around the ambition of developed countries’ emissions cut pledges which countries more vulnerable to climate change are trying to increase.

Another sticking point remains over accounting rules for future carbon market mechanisms. A senior negotiator said Brazil still had concerns over the rules aimed at avoiding double counting emissions cuts.

“There are still a range of possible outcomes and Brazil continues to work constructively with other parties to find a workable pathway forward,” Antonio Marcondes, Brazil’s chief negotiator, told Reuters.

Countries are on a self-imposed deadline to produce a “rulebook” to flesh out details of the 2015 Paris Agreement, which aims to limit the global temperature rise to less than 2 degrees Celsius and which comes into force in 2020.

Talks in Katowice have been going on for two weeks and were due to end on Dec. 14 but they have been clouded by political divisions.

A rift last week over how to express the importance of a U.N. commissioned report on keeping global warming within a 1.5 degrees Celsius limit appears to have been calmed, with language changed to “note” rather than “welcome” the report.

Talks have also faltered over increasing finance for climate adaptation for poorer countries. Governments have already agreed to raise $100 billion a year by 2020, but developing countries wanted more.

The latest text says a meeting in 2020 will start “deliberations” to increase that amount.